It's unlikely that the film caps were added to increase the value of the
electrolytics appreciably. Compare the value of the film caps to the 10% (or
more) tolerance of the electrolytics. It's done in a bid to combine the
quality of the film cap with the capacitance of the electrolytic. The sound
of such parallel circuits is pretty unpredictable though - needs
experimentation when you change types of components. It's not unusual for an
electrolytic to sound better alone than with an extra film cap on top.

Intertechnik (http://www.intertechnik.de/) sells "audyn" branded film caps
up to rather large values. Very decent sounding parts.

The largest film caps are from http://www.eci-capacitors.com/. Never tried
them though.

Matching to within 10% (eg +/-5% tolerance) is desirable, to make sure the
speakers (well, ignoring differences between drive units) remain within 1dB
of eachother.